Oxide-coated Al-Cu-based nanoparticles for enhanced solar water heating

We report the use of oxide-coated Al-Cu nanoparticles for enhanced solar water heating purposes. Both Al and Cu are earth-abundant metals, so they are chosen in this work. Furthermore, Al- and Cu-based nanoparticles have substantial absorption cross-sections in UV, visible, and some parts of the near-infrared region (∼300–1100 nm). This makes these nanoparticles useful in solar water heating applications. An aqueous synthesis approach, which yields oxide-coated Al-Cu-based nanoparticles, is used since it is scalable and eco-friendly. The effects of particle loading between 0.025–0.1 wt% in water, for use as a nanofluid, are tested under an infrared source. The oxide-coated Al-Cu nanoparticles are mostly cubic in morphology. The particles are stable in the nanofluid with zeta potential values >30 mV. On dispersing 0.075 wt% of these nanoparticles in water, a 14–16 % enhancement in the saturation temperature is obtained. This implies that the heating kinetic constants are increased by ∼15 % upon addition of these nanoparticles to water. The scattering and absorption cross-sections for the Al-Cu-oxide based nanoparticle system were determined computationally by solving the Maxwell’s equations. The peak scattering cross-section was found to occur at a wavelength of 728 nm for a particle size of 50 nm. The values obtained computationally were used as inputs to solve the energy balance equations for simulating a water heating setup. A maximum temperature of 347.5 K is predicted for a volume of 500 ml water over a 12-hour solar heating time period, with an initial ambient temperature of 305 K. These values are commensurate with the experimental data, thus validating the model’s accuracy. These results suggest that Al-Cu-based nanoparticles would be promising candidates for use in solar water heating and thermal nanofluid applications.